Fuel cells use the chemical conversion of a fuel into water with the aid of oxygen to generate electrical energy. For this purpose, fuel cells include the so-called membrane electrode assembly (MEA) as a core component, which is an assembly of an ion-conducting (usually proton-conducting) membrane and an electrode (anode and cathode) situated on both sides of the membrane. In addition, gas diffusion layers (GDL) may be situated on both sides of the membrane electrode assembly, on the sides of the electrodes facing away from the membrane. The fuel cell is generally formed by a large number of MEAs situated in a stack, whose electrical powers add up. Bipolar plates (also referred to as flow field plates) are situated between the individual membrane electrode assemblies and ensure a supply of operating agents, i.e., reactants, to the individual cells and are usually also used for cooling. In addition, the bipolar plates ensure an electrically conductive contact to the membrane electrode assemblies.
During the operation of a polymer electrolyte membrane (PEM) fuel cell, the fuel, in particular hydrogen H2 or a hydrogen-containing gas mixture is supplied via a flow field of the bipolar plate, which is open on the anode side, to the anode, where an electrochemical oxidation of H2 to H+ takes place with the discharge of electrons. A (water-bound or water-free) transfer of protons H+ from the anode space to the cathode space takes place via the electrolyte or the membrane, which separates and electrically insulates the reaction spaces from each other in a gas-tight manner. The electrons provided at the anode are supplied to the cathode via an electric line. Oxygen or an oxygen-containing gas mixture (for example air) is supplied to the cathode via a flow field of the bipolar plate, which is open on the cathode side, so that a reduction from O2 to O2− takes place with the absorption of the electrons. At the same time, in the cathode space, the oxygen anions react with the protons transferred via the membrane, forming water.
A fuel cell stack includes at least two main channels for each operating agent (anode operating gas, cathode operating gas, coolant), namely at least one supplying main channel and at least one discharging main channel in each case. The main channels extend through the entire stack and supply the individual fuel cells with the operating agents (also referred to as operating media).
To supply a fuel cell stack with its operating agents, the fuel cell stack includes an anode supply system on the one hand and a cathode supply system on the other hand. The anode supply system includes an anode supply path for supplying an anode operating gas to the anode spaces and an anode exhaust gas path for discharging an anode exhaust gas from the anode spaces. The anode supply path is fluid-conductively connected to the corresponding supplying main channel for the anode operating gas, and the anode exhaust gas path is fluid-conductively connected to the corresponding discharging main channel of the stack. Likewise, the cathode supply system includes a cathode supply path for supplying a cathode operating gas to the cathode spaces and a cathode exhaust gas path for discharging a cathode exhaust gas from the cathode spaces of the fuel cell stack. A cathode supply path is fluid-conductively connected to the corresponding supplying main channel for the cathode operating gas, and the cathode exhaust gas path is fluid-conductively connected to the corresponding discharging main channel of the stack. A cooling circuit for the fuel cell stack is connected to the corresponding supplying and discharging main channels of the fuel cell stack for the purpose of conducting a coolant through the stack and dissipating the reaction heat.
When a fuel cell system is used, for example in a motor vehicle, a considerable quantity of individual fuel cells is needed to be able to provide the desired electrical energy. The problem arises that the length of the fuel cell stack increases significantly in the stack direction, and it becomes difficult to uniformly supply the operating gases, in particular the anode operating gas, to the particular fuel cell units.
It is therefore known to use a fuel cell system which is constructed from a plurality of fuel cell stacks. The plurality of fuel cell stacks is situated either in series or in parallel to each other.
DE 10 2004 060 526 A1 discloses a plurality of fuel cell stacks situated in series, in which the fuel cell stacks are connected to each other by their facing end plates. This gives rise to the problem that the length of the fuel cell stack increases significantly in the stack direction, and it becomes difficult to uniformly supply the operating agents to the individual fuel cell units.
In contrast, EP 1 127 382 B1 and DE 100 41 532 B4 disclose a plurality of fuel cell stacks which are situated in parallel to each other and are supplied with operating media via shared supply lines to the main channels.
To optimize the supply of operating media, DE 11 2004 001 759 T5 describes a media adapter plate for distributing operating media to multiple parallel-connected fuel cell stacks for the purpose of creating a more compact power generating system and to uniformly distribute and collect or combine reactants for each fuel cell stack in one power generating system. Identical fuel cell stacks are situated next to each other for this purpose.